This invention relates to high power (nonlinear) testing of RF (radio frequency) transistors (DUT) in the frequency and time domain (see ref. 1) using Load Pull. Load pull is the method by which the load impedance presented to the DUT at a given frequency is changed systematically and the DUT performance is registered, with the objective to find an optimum depending on the overall design objectives (see ref. 1). This may be maximum power, efficiency, linearity or else. The same is valid for the source side of the DUT. Passive (slide screw) tuners are used to create the various impedances presented to the DUT (see ref. 2) for frequencies above 100 MHz; these tuners are very long, because the tuning probe must travel along the airline at least one half of a wavelength (λ/2) to cover 360° of reflection factor area. At 100 MHz this is 1.5 meters, at 10 MHz this is 15 meters. For the manufacturing precision required for this type of machine, this is an extreme read impossible challenge. At lower frequencies the situation is even more critical. For frequencies between 10 MHz and approximately 200 MHz another type of tuner, the “low frequency tuner”, is used (see ref. 3). This latter tuner structure uses commercially available variable (rotary blade) capacitors and fixed lengths of coaxial cable (FIG. 1). All items in FIG. 1 are not referred to in this specification.
Rotary capacitors (29) (see ref. 4, FIG. 2) are made using sets of parallel metallic blades (26, 27) which are isolated electrically (28) and are inserted into each other inter-digitally by rotating (201) one set (26). Other type of variable capacitors can also be used, such as coaxial type capacitors, appropriate for frequencies at the high end of the frequency specter, whereby concentric tubes are inserted from opposite directions (see FIG. 11).